This invention relates to an optical transmission module for optical communication, and particularly to an optical transmission module used for a transmission portion of an optical transceiver having a high transfer rate (10 Gbit/s, for example).
An optical transmission module using a semiconductor laser is one of the key devices of transceivers for optical fiber transfer. An operation speed of optical transmission modules has been improved with recent popularization of broadband networks and optical transmission modules having a transfer rate of up to 10 Gbit/s have now been used widely. The optical transmission modules suitable for this application are strongly required to possess small size and low cost and to achieve high transmission waveform quality.
Optical transmission modules directed to improve high frequency characteristics are disclosed in JP-A-2001-257412 (corresponding to U.S. Pat. No. 6,823,145) and JP-A-2001-308130 (corresponding to U.S. Pat. No. 6,507,111). These patent references JP-A-2001-257412 and JP-A-2001-308130 describe the optical transmission modules that simultaneously reduce a small signal reflection coefficient (S11) at a characteristic impedance of 50 Ohms on the high frequency input side and secure a 3 dB band in a small signal passage characteristic (S21) of an optical modulator by optimizing the relation of inductances between a first bonding wire for connecting a modulator and a signal line of an electro-absorption modulator type optical modulator integrated laser diode and a second bonding wire for connecting the modulator and a terminal resistor.
As disclosed in JP-A-2001-257412 and JP-A-2001-308130, one of the ends of the terminal resistor is connected by the bonding wire to the modulator but the other end is connected to a ground electrode through a ground via-hole, or the like, without being connected to the modulator in the optical transmission module according to the related art. A cathode electrode or anode electrode of an electro-absorption type modulator is disposed on the chip back surface of the modulator integrated laser diode.
JP-A-2005-353910 (corresponding to US Patent Publication No. 2005/275053) describes, on the other hand, an electro-absorption modulator type optical modulator integrated laser diode having a different device structure. An optical modulator element and a laser diode element are arranged on a semi-insulating semiconductor board and an anode of each device is electrically isolated from its cathode so that driving by a single power source can be achieved.